1. Field of the Invention
The presently disclosed subject matter is related to a color imaging device, and in particular, to a color imaging device that can reduce occurrence of color moire and achieve high resolution.
2. Description of the Related Art
In a single-panel type color imaging device, since a one-colored color filter is set on each pixel, each pixel has only color information of one color. Therefore, because an output image of a single-panel type color imaging device is a RAW image (mosaic image), a multi-channel image is obtained by processing to interpolate a pixel of a missing color from the surrounding pixel (synchronization processing). In this case, there is a problem of a reproduction characteristic of a high-frequency image signal. In the color imaging device, aliasing is easily generated in a captured image as compared with an imaging device for black-and-white. Therefore, there is an issue in which it is important that high-resolution is achieved by expanding a reproduction band while suppressing occurrence of color moire (false color).
In a primary color system Bayer array that is a color array of a color filter that is widely used in the single-panel type color imaging device, green (G) pixels are arranged in a checkered pattern, and red (R) pixels and blue (B) pixels are arranged line-sequentially. Therefore, there is a problem of reproduction accuracy when a high frequency signal is generated in the diagonal directions for the G signal and reproduction accuracy when a high frequency signal is generated in the horizontal and vertical directions for the R and B signals.
In a case in which a black-and-white vertical stripe pattern (high frequency image) as illustrated in (A) in FIG. 22 enters a color imaging device having a color filter of a Bayer array illustrated in (B) in FIG. 22, when the entered pattern is allocated to a Bayer color array and compared for each color, as illustrated in (C) to (E) in FIG. 22, a color image of R in light flat, a color image of B in dark flat, and a color image of G in light/dark mosaic are generated. The black-and-white image in which there is no concentration difference (level difference) between R, G, and B, originally, becomes in a state of being colored depending on a color array and an input frequency.
Similarly, in a case in which a diagonal black-and-white high frequency image as illustrated in (A) in FIG. 23 enters an imaging device including color filters of a Bayer array illustrated in (B) in FIG. 23, when the entered pattern is allocated to a Bayer color array and compared for each color, as illustrated in (C) to (E) in FIG. 23, color images of R and B in light flat and a color image of G in dark flat are generated. When it is assumed that a black value is 0 and a white value is 255, the diagonal black-and-white high frequency image becomes in green because only G becomes 255. As described above, in the Bayer array, the diagonal high frequency image cannot be reproduced appropriately.
Generally, in an imaging apparatus that uses a single-panel type color imaging device, an optical low pass filter that is constituted by a birefringence material such as crystal is arranged in the front of the color imaging device, and a high frequency is avoided so as to be optically reduced. However, in this method, coloring by the folding of the high frequency signal can be reduced, but there is a problem that the resolution is reduced due to the adverse effect.
In order to solve such a problem, a color imaging device has been proposed in which a color filter array of the color imaging device is a three-colors random array that satisfies an array restriction condition in which a given focused pixel is adjacent to any of three colors including a color of the focused pixel on the four sides of the focused pixel (Japanese Patent Application Laid-Open No. 2000-308080).
In addition, an image sensor of a color filter array has been proposed that includes a plurality of filters having different spectral sensitivities, and in which a first filter and a second filter out of the filters are alternately arranged in one diagonal direction of a pixel grid of the image sensor in a first certain cycle and are alternately arranged in the other diagonal direction in a second certain cycle (Japanese Patent Application Laid-Open No. 2005-136766).
In addition, a color array has been proposed in which, in a color solid imaging device of three primary colors of R, G, and B, appearance probabilities of R, G, and B are equalized and a given straight line (horizontal, vertical, or diagonal straight line) on an imaging surface passes through all of the colors by arranging sets of 3 pixels in which R, G, and B are horizontally arranged so that the sets are shifted in a zig-zag manner (Japanese Patent Application Laid-Open No. 11-285012).
In addition, a color imaging device has been proposed in which R and B out of three primary colors of R, G, and B are arranged in the horizontal direction and the vertical direction in every three pixels, and G is arranged between R and B (Japanese Patent Application Laid-Open No. 8-023543).
In addition, Japanese Patent Application Laid-Open No. 2009-027684 suggests a color array in which: in a color solid imaging device of three primary colors of R, G, and B, a color filter array is divided into four areas by the X axis and Y axis passing through the center; R, G, and B are arranged in a Bayer array in each area; and R, G, and B of each area has the X axis mirror symmetry pattern and the Y axis mirror symmetry pattern. In the color filter array described in this Japanese Patent Application Laid-Open No. 2009-027684, the one or more Gs are arranged on the horizontal direction (X axis) and vertical direction (Y axis) of the color filter array and each line of the diagonal directions.